Electromagnetic Waves | Physics JEE Main questions with Solutions

Q 1 :

Arrange the following in the ascending order of wavelength:

A. Gamma rays ( $λ_{1}$ )

B. x-rays ( $λ_{2}$ )

C. Infrared waves ( $λ_{3}$ )

D. Microwaves ( $λ_{4}$ )

Choose the most appropriate answer from the options given below [2024]

$λ_{4} < λ_{3} < λ_{1} < λ_{2}$
$λ_{2} < λ_{1} < λ_{4} < λ_{3}$
$λ_{4} < λ_{3} < λ_{2} < λ_{1}$
$λ_{1} < λ_{2} < λ_{3} < λ_{4}$

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(4)

Order of wavelength

gamma rays < x-rays < infrared < microwaves

$\Rightarrow λ_{1} < λ_{2} < λ_{3} < λ_{4}$

Q 2 :

Match List-I with List-II:

List-I

(EM-Wave)

List-II

(Wavelength Range)

A Infra-red (I) $10^{- 3}$ nm

B Ultraviolet (II) 400 nm to 1 nm

C X-rays (III) 1 mm to 700 nm

D Gamma rays (IV) 1 nm to $10^{- 3}$ nm

Choose the correct answer from the options give below [2024]

(A)-(I), (B)-(III), (C)-(II), (D)-(IV)
(A)-(IV), (B)-(III), (C)-(II), (D)-(I)
(A)-(III), (B)-(II), (C)-(IV), (D)-(I)
(A)-(II), (B)-(I), (C)-(IV), (D)-(III)

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(3)

Infrared is the least energetic thus having biggest wavelength $(λ)$ and gamma rays are most energetic thus having smallest wave length $(λ)$ .

Q 3 :

Arrange the following in the ascending order of wavelength ( $λ$ )

(A) Microwaves ( $λ_{1}$ ) (B) Ultraviolet rays ( $λ_{2}$ )

(C) Infrared rays ( $λ_{3}$ ) (D) X-rays ( $λ_{4}$ )

Choose the most appropriate answer from the options given below: [2025]

$λ_{4} < λ_{3} < λ_{2} < λ_{1}$
$λ_{3} < λ_{4} < λ_{2} < λ_{1}$
$λ_{4} < λ_{2} < λ_{3} < λ_{1}$
$λ_{4} < λ_{3} < λ_{1} < λ_{2}$

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(3)

Q 4 :

Given below are two statements: One is labelled as Assertion (A) and other is labelled as Reason (R).

Assertion (A) : Electromagnetic waves carry energy but not momentum.

Reason (R) : Mass of a photon is zero.

In the light of the above statements, choose the most appropriate answer from the options given below: [2025]

(A) is true but (R) is false.
(A) is false but (R) is true.
Both (A) and (R) are true but (R) is not the correct explanation of (A).
Both (A) and (R) are true and (R) is the correct explanation of (A).

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(2)

EM wave carry both energy and momentum. Restmass of photon is zero.

Q 5 :

If an optical medium possesses a relative permeability of $\frac{10}{π}$ and relative permittivity of $\frac{1}{0.0885}$ , then the velocity of light is greater in vacuum than that in this medium by _______ times. ( $μ_{0} = 4 π \times 10^{- 7} H / m, \in_{0} = 8.85 \times 10^{- 12} F / m, c = 3 \times 10^{8} m / s$ ) [2025]

0%

(6)

Since velocity of light in terms of $μ$ and E is

$v = \frac{1}{\sqrt{μ ε}} = \frac{1}{\sqrt{μ_{0} μ_{r}}} \times \frac{1}{\sqrt{ε_{0} ε_{r}}} = \frac{1}{\sqrt{μ_{r} ε_{r}}} \times \frac{1}{\sqrt{μ_{0} ε_{0}}}$

$v = \frac{c}{\sqrt{μ_{r} ε_{r}}} = \frac{c}{\sqrt{\frac{10}{π} \times \frac{1}{0.0885}}} = \frac{c}{\sqrt{36}} = \frac{c}{6}$

$\Rightarrow c = 6 v$

Velocity of light in vacuum is greater by 6 times the velocity of light in medium.

Q 6 :

The electric field and magnetic field components of an electromagnetic wave going through vacuum is described by $E_{x} = E_{0} \sin (k z - ω t), B_{x} = B_{0} \sin (k z - ω t)$ . Then the correct relation between $E_{0}$ and $B_{0}$ is given by [2023]

$E_{0} B_{0} = ω k$
$E_{0} = k B_{0}$
$k E_{0} = ω B_{0}$
$ε E_{0} = ω B_{0}$

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(3)

$C = \frac{ω}{k} = \frac{E_{0}}{B_{0}}$

Q 7 :

Match List-I with List-II. [2023]

List I List II

A. Microwaves I. Physiotherapy

B. UV rays II. Treatment of cancer

C. Infra-red rays III. Lasik eye surgery

D. X-rays IV. Aircraft navigation

Choose the correct answer from the option given below:

A-II, B-IV, C-III, D-I
A-IV, B-I, C-II, D-III
A-IV, B-III, C-I, D-II
A-III, B-II, C-I, D-IV

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(3)

(Theoretical)

A. Microwaves → IV B. UV rays → III

C. Infra-red rays → I D. X-rays → II

Q 8 :

Match the List-I with List-II: [2023]

List I List II

A. Microwaves I. Radio active decay of the nucleus

B. Gamma rays II. Rapid acceleration and deceleration of electron in aerials

C. Radio waves III. Inner shell electrons

D. X-rays IV. Klystron valve

Choose the correct answer from the option given below:

A-I, B-II, C-III, D-IV
A-IV, B-I, C-II, D-III
A-I, B-III, C-IV, D-II
A-IV, B-III, C-II, D-I

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(2)

1. Klystron valve used to produce Microwave

2. Gamma ray → Radioactive decay

3. Radio wave → Rapid acceleration and deceleration of electrons in aerials

4. X-ray → Inner shell electrons

Q 9 :

If a source of electromagnetic radiation having power 15 kW produces $10^{16}$ photons per second, the radiation belongs to a part of spectrum is (Take Planck constant $h = 6 \times 10^{- 34}$ Js) [2023]

Micro waves
Ultraviolet rays
Gamma rays
Radio waves

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(3)

$Energy of one photon = \frac{Power}{photon frequency}$

$E = h ν = \frac{15 \times 10^{3}}{10^{16}}$

$\Rightarrow ν = \frac{15 \times 10^{- 13}}{6 \times 10^{- 34}} = 2.5 \times 10^{21}$

Q 10 :

If $\vec{E}$ and $\vec{K}$ represent electric field and propagation vectors of the EM waves in vacuum, then magnetic field vector is given by ( $ω$ - angular frequency) [2023]

$\frac{1}{ω} (\vec{K} \times \vec{E})$
$ω (\vec{K} \times \vec{E})$
$\vec{K} \times \vec{E}$
$ω (\vec{E} \times \vec{K})$

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(1)

Magnetic field vector will be in the direction of $\vec{K} \times \vec{E}$

$Magnitude of B = \frac{E}{C} = \frac{K}{ω} E$

or $\vec{B} = \frac{1}{ω} (\vec{K} \times \vec{E})$

Topic Question Set

Q 1 :

Arrange the following in the ascending order of wavelength:

A. Gamma rays ( $λ_{1}$ )

B. x-rays ( $λ_{2}$ )

C. Infrared waves ( $λ_{3}$ )

D. Microwaves ( $λ_{4}$ )

Choose the most appropriate answer from the options given below [2024]

Q 2 :

Match List-I with List-II:

List-I

(EM-Wave)

List-II

(Wavelength Range)

A Infra-red (I) $10^{- 3}$ nm

B Ultraviolet (II) 400 nm to 1 nm

C X-rays (III) 1 mm to 700 nm

D Gamma rays (IV) 1 nm to $10^{- 3}$ nm

Choose the correct answer from the options give below [2024]

Q 3 :

Arrange the following in the ascending order of wavelength ( $λ$ )

(A) Microwaves ( $λ_{1}$ ) (B) Ultraviolet rays ( $λ_{2}$ )

(C) Infrared rays ( $λ_{3}$ ) (D) X-rays ( $λ_{4}$ )

Choose the most appropriate answer from the options given below: [2025]

0%

Q 6 :

The electric field and magnetic field components of an electromagnetic wave going through vacuum is described by $E_{x} = E_{0} \sin (k z - ω t), B_{x} = B_{0} \sin (k z - ω t)$ . Then the correct relation between $E_{0}$ and $B_{0}$ is given by [2023]

Q 7 :

Match List-I with List-II. [2023]

List I List II

A. Microwaves I. Physiotherapy

B. UV rays II. Treatment of cancer

C. Infra-red rays III. Lasik eye surgery

D. X-rays IV. Aircraft navigation

Choose the correct answer from the option given below:

Q 9 :

If a source of electromagnetic radiation having power 15 kW produces $10^{16}$ photons per second, the radiation belongs to a part of spectrum is (Take Planck constant $h = 6 \times 10^{- 34}$ Js) [2023]

Q 10 :

If $\vec{E}$ and $\vec{K}$ represent electric field and propagation vectors of the EM waves in vacuum, then magnetic field vector is given by ( $ω$ - angular frequency) [2023]

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	List-I (EM-Wave)		List-II (Wavelength Range)
A	Infra-red	(I)	$10^{- 3}$ nm
B	Ultraviolet	(II)	400 nm to 1 nm
C	X-rays	(III)	1 mm to 700 nm
D	Gamma rays	(IV)	1 nm to $10^{- 3}$ nm

	List I		List II
A.	Microwaves	I.	Physiotherapy
B.	UV rays	II.	Treatment of cancer
C.	Infra-red rays	III.	Lasik eye surgery
D.	X-rays	IV.	Aircraft navigation